Field of the Invention
The present invention relates to a vapor generator and, more particularly, to a vapor generator for use in a cooler or heater of absorption type or to a steam generator which generates steam for air conditioning purpose.
A vapor generator generally referred to as "flue tube type generator", having burners, flue and tubes, has been known as a typical example of the vapor generators of the kind mentioned above.
In this type of vapor generator, the flame formed by burning of a fuel atomized from burners, as well as the gas of high temperature produced as a result of burning, passes through the flue to heat and evaporate a medium which is stored in a drum around the flue and also in the tubes.
In a conventional flue tube type vapor generator, a plurality of vertically extending tubes are arranged in rows such that tubes of one row are staggered from those of adjacent rows when viewed in plan. In other words, each tube of second row appears through the gap between each pair of adjacent tubes of first row, when viewed in the direction of flow of the gas. One problem of such an arrangement of the tubes resides in the fact that the tubes of the first row restrict the area of passage for the gas. As a result, the flow velocity of the gas is through the restricted passages formed between respective two adjacent tubes of the first row is increased, and the gas of increased velocity is directed to the center of each tube of the second row due to a nozzle action performed by each restricted flow passage. Consequently, the tubes of the second row are locally overheated at their central portions to cause a rapid local corrosion at such central portions. Another problem encountered by this conventional flue tube type resides in the fact that the exchange of heat between the medium in the drum around the flue and the flame and high-temperature gas around the flame is made only across the smooth wall defining the flue, so that heat is exchanged only at a small rate between the gas around the flame and the medium in the drum. Consequently, the gas contacts the tubes of the first row while it is still hot, i.e. before making substantial temperature drop. Thus the tubes of the first row are also overheated locally to exhibit rapid corrosion. This problem will be overcome if there is an ample distance between the flame and the tubes of the first row. Such arrangement, however, will increase the overall size of the vapor generator.